1. Field of the Invention
The present invention relates to a dental catalyst for chemical polymerization used in the field of dental therapy, to a dental adhesive composition using the dental catalyst for chemical polymerization, and to use of the dental curable composition.
2. Description of Prior Arts
A method of curing a polymerizable monomer by using a catalyst for polymerization has been widely employed in the dental field by using, for example, a dental cement, a dental adhesive, a composite resin, a dental self-curing resin, a dental pretreatment material, etc.
These materials require catalysts for polymerization of different kinds depending upon their compositions, objects of use and required properties. The catalysts for polymerization may be divided into those for photo polymerization and those for chemical polymerization. It, however, becomes necessary to use a catalyst for chemical polymerization when the curable composition contains much filler which permits light to pass through little or when the catalyst is used for such applications where it cannot be irradiated with light. Further, the dental adhesive and the pretreatment material, in many cases, require the use of a catalyst for chemical polymerization depending upon the kind of the dental material that is to be adhered. Besides, the catalyst for photo polymerization must be irradiated with light by using a dedicated device. From the standpoint of easy operation, therefore, it is often desired to use the catalyst for chemical polymerization.
In restoring a tooth damaged by, for example, decaying or accident by directly filling the cavity of the tooth with a paste-like dental restorative as represented by a composite resin or a composite polymer followed by curing (direct restoring method), there has been used, as an adhesive (adhesive for directly restoring the teeth), a bonding agent comprising chiefly a polymerizable monomer which contains an acidic group-containing polymerizable monomer. As the bonding agent, there has been developed an excellent material which does not require the pretreatment that was so far needed (Japanese Unexamined Patent Publications (Kokai) Nos. 263604/1997 and 245525/1998). The above bonding agent, however, uses a particular catalyst for photo polymerization, and it has been desired to omit the operation for irradiation with light in order to simplify the adhering operation. Besides, when the above bonding agent is used in combination with a dental restorative of the chemical polymerization type, the unreacted acidic group-containing polymerizable monomer in the bonding agent reacts with an amine component in the organic peroxide/tertiary amine catalyst that is usually used as a catalytic component for chemical polymerization of the dental restorative. As a result, a sufficient degree of adhering strength is not obtained and, hence, the dental restoratives to be used in combination are limited to those of the photo-curable type only, which is a problem.
Further, according to a restoring method (indirect restoring method) by which a dental restorative such as an inlay or a crown prepared in advance outside the oral cavity by using a metal or a ceramic material, is adhered to a tooth, there is used, as an adhesive, a dental adhesive cement such as an adhesive resin cement or a resin-modified glass ionomer cement comprising, chiefly, a polymerizable monomer that contains an acidic group-containing polymerizable monomer and an organic or inorganic filler. These cements, however, often contain fillers in large amounts or are used in combination with metal materials that do not permit light to pass through. It therefore becomes necessary to use a catalyst for chemical polymerization that is capable of executing the polymerization in a dark place at ambient temperature.
A variety of catalysts for chemical polymerization have heretofore been proposed. Examples of the catalyst for chemical polymerization include those of {circle around (1)} a system using a trialkylboran or a partial oxide thereof (Japanese Unexamined Patent Publication (Kokai) No. 108102/1982), {circle around (2)} a redox-type cold self-polymerization initiator such as a system of a combination of an organic peroxide and a cobalt salt or a manganese salt or a system of a combination of an organic peroxide and a tertiary amine (Japanese Unexamined Patent Publication (Kokai) No. 92884/1976), and a system of a combination of hydrogen peroxide and an Fe2+ compound, {circle around (3)} a system of a barbituric acid, a Cu2+ compound and a Clxe2x88x92 compound (Japanese Unexamined Patent Publication (Kokai) No. 295013/1993), and {circle around (4)} a system of a combination of an aryl borate compound and an acidic compound (Japanese Unexamined Patent Publication (Kokai) No. 309811/1997) and a system of a combination of an aryl borate compound, an acidic compound and a transition metal compound (Japanese Unexamined Patent Publication (Kokai) No. 227325/1997). Among them, some catalysts have been put into a practical use.
Japanese Unexamined Patent Publication (Kokai) No. 169535/2000 discloses a self-curing resin composition that cures at ambient temperature obtained by blending a composition of a combination of (A) a polymerizable unsaturated compound, (B) a radical-generating catalyst, and a polymerization initiator of an organoboron compound represented by the following general formula (I), 
with an acidic compound or with (A) the acidic polymerizable unsaturated compound. There has been described that this resin composition is effective in the FRP hand-lay-up molding, or in the FRP lining work in the fields of construction and civil engineering.
The system {circle around (1)} which uses the trialkylboran or the partial oxide thereof is an excellent catalyst for chemical polymerization which is very active but is chemically very unstable. Therefore, this catalyst must be packaged separately from other components, must be picked up in suitable amounts just before it is used and must be mixed with other monomer components, requiring cumbersome operation, which is a drawback.
The catalyst {circle around (2)} for chemical polymerization of a combination of the organic peroxide and the tertiary amine and the catalyst {circle around (3)} for chemical polymerization of the barbituric acid system, are most generally used in the field of dental materials from the standpoint of low beneficial/harmful action to the living bodies and easy availability involving, however, problems as pointed out below.
That is, the catalyst for chemical polymerization of a combination of the organic peroxide and the tertiary amine, involves such problems as tinting the cured product due to oxidation of the amine compound and discoloration, and impairing the polymerization due to oxygen and acidic components (the acidic component here produces a quaternary salt which does not exhibit reducing ability upon reacting with the tertiary amine). The problem of tinting or discoloration causes the color tone to become different from that of a natural tooth when the catalyst is used for a dental restorative as represented by a composite resin, and deteriorates the aesthetic value. The problem of impairing the polymerization means that the catalyst cannot be used for the dental adhesive that uses the acidic group-containing polymerizable monomer as an essential component. The catalyst for chemical polymerization of the barbituric acid type has such problems as difficulty in controlling the curing time and poor preservation stability.
The catalyst {circle around (4)} for chemical polymerization using the aryl borate is easy to handle, does not cause the cured product to be tinted or discolored, and exhibits excellent preservation stability without, however, exhibiting sufficient activity for polymerization. Therefore, further improved activity has been desired.
As described above, no dental catalyst for chemical polymerization has yet been known, which is chemically stable, easy to handle, highly active, less subject to be impaired by polymerization, and does not cause the cured product to be tinted or discolored.
It is therefore an object of the present invention to provide a dental catalyst for chemical polymerization having the above excellent features.
In order to accomplish the above-mentioned object, the present inventors have conducted keen study. As a result, the present inventors have discovered that the activity for polymerization is greatly enhanced when an aryl borate compound and an acidic compound are used in combination with a particular oxidizing agent, that the dental curable composition using the above catalyst for chemical polymerization exhibits excellent features as an adhesive, as a pretreatment material or as a restorative, and have completed the present invention.
That is, a first invention is concerned with a dental catalyst for chemical polymerization comprising an aryl borate compound, an acidic compound and an organic peroxide, without substantially containing amine compound which exhibits a catalytic action. The dental catalyst for chemical polymerization of the present invention does not substantially contain amine compound and, hence, does not cause the cured product to be tinted or discolored. Besides, the catalyst is easy to handle, exhibits high activity for polymerization even in the presence of oxygen or an acidic compound, and imparts a suitable degree of surplus operation time. Among the catalysts for dental chemical polymerization of the present invention, the one containing a metal compound for promoting the decomposition of the organic peroxide, exhibits a particularly high polymerizing activity. When the catalyst containing the acidic group-containing polymerizable monomer as an acidic compound, is used as a catalyst for polymerizing the dental curable composition that contains the polymerizable monomer as an essential component, there is no need of adding any other acidic compound, and no acidic compound elutes out from the obtained cured product when it is used.
Though not stuck to the theory, it is considered that in the dental catalyst for chemical polymerization of the present invention, the aryl borate compound is decomposed with the acidic compound to thereby form an aryl borane compound which is then oxidized with oxygen present in the atmosphere to form polymerizable radicals and is further oxidized with an organic peroxide to form more radicals in the curable composition containing less oxygen, to thereby serve as a highly active catalyst for chemical polymerization. Upon containing a metal compound that promotes the decomposition of the organic peroxide, further, oxidation of the aryl borane compound with the organic peroxide is promoted lending the catalyst itself well for use as a more active catalyst for chemical polymerization.
A second invention is concerned with a dental curable composition containing a polymerizable monomer and the dental catalyst for chemical polymerization of the present invention. The dental curable composition of the present invention has a feature in that it undergoes the polymerization at ambient temperature even in a dark place to give an excellently cured product. Further, a dental adhesive composition which further contains a photopolymerization initiator is a curable composition of the so-called dual cure type and has a feature in that it finds a wide range of clinical use.
A third invention is concerned with an adhesive for directly restoring the teeth, comprising a dental curable composition of the present invention containing 100 parts by weight of a polymerizable monomer which contains an acidic group-containing polymerizable monomer, 0.01 to 10 parts by weight of an aryl borate compound, 0.01 to 10 parts by weight an organic peroxide, 1 to 20 parts by weight of a multi valent metal ion-eluting filler and/or 2 to 30 parts by weight of water. The adhesive for directly restoring the teeth (bonding agent) of the present invention strongly adheres to both the dentin and the enamel without the need of pretreating the tooth tissue, can be applied without the need of irradiation with light, and can be used both as the dental restorative of the photo-curing type and the dental restorative of the chemically curing type, which is an excellent feature that could not be found with the existing bonding agents.
Further, a fourth invention is concerned with an adhesive for indirectly restoring the teeth, comprising a dental curable composition of the present invention containing 100 parts by weight of a polymerizable monomer which contains an acidic group-containing polymerizable monomer, 0.01 to 10 parts by weight of an aryl borate compound, 0.01 to 10 parts by weight an organic peroxide, and 50 to 900 parts by weight of a filler.
The adhesive for indirectly restoring the teeth of the present invention has a feature in that it adheres will to both the enamel and the dentin.
A fifth invention is concerned with a dental restorative comprising a dental curable composition of the invention containing a filler in an amount of 50 to 900 parts by weight per 100 parts by weight of the whole polymerizable monomers. The dental restorative is the one that can be used as a material which substitutes for damaged portion of the tooth, and that gives a highly strong cured product without tint or discoloration, making it possible to accomplish a highly aesthetic and highly reliable restoration.
A sixth invention is concerned with a dental pretreatment material comprising a dental curable composition of the present invention which contains an acidic group-containing polymerizable monomer, an aryl borate compound, an organic peroxide and water. Even when the adhesive of the photo polymerization type or the adhesive of the chemical polymerization type is used, the dental pretreatment material of the present invention gives a highly strong adhesiveness to both the enamel and the dentin through one time of application, and maintains a high degree of safety.